Organolanthanide‐Mediated Intermolecular Hydroamination of 1,3‐Dienes: Mechanistic Insights from a Computational Exploration of Diverse Mechanistic Pathways for the Stereoselective Hydroamination of 1,3‐Butadiene with a Primary Amine Supported by an ansa‐Neodymocene‐Based Catalyst

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Abstract
The complete catalytic reaction course for the organolanthanide‐mediated intermolecular hydroamination of 1,3‐butadiene and n‐propylamine by an archetypical [Me2Si(η5‐Me4C5)2NdCH(SiMe3)2] precatalyst was critically scrutinized by employing a reliable gradient‐corrected DFT method. A free‐energy profile of the overall reaction is presented that is based on the thorough characterization of all crucial elementary steps for a tentative catalytic cycle. A computationally verified, revised mechanistic scenario is proposed which is consistent with the experimentally derived empirical rate law and accounts for crucial experimental observations. It involves kinetically mobile reactant association/dissociation equilibria and facile, reversible intermolecular diene insertion into the Nd–amido bond, linked to turnover‐limiting protonolysis of the η3‐butenyl–Nd functionality. The computationally predicted effective kinetics (Δ${H{{{\ne}\hfill \atop {\rm tot}\hfill}}}$=11.3 kcal mol−1, Δ${S{{{\ne}\hfill \atop {\rm tot}\hfill}}}$=−35.7 e.u.) are in reasonably good agreement with experimental data for the thoroughly studied hydroamination of alkynes. The thermodynamic and kinetic factors that determine the almost complete regio‐ and stereoselectivity of the mechanistically diverse intermolecular 1,3‐diene hydroamination have been unraveled. The present computational study complements experiments because it allows, first, a more detailed understanding and a consistent rationalization of the experimental results for the hydroamination of 1,3‐dienes and primary amines and, second, enhances the insights into general mechanistic aspects of organolanthanide‐mediated intermolecular hydroamination.

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